1. Field of the Invention
The present invention relates to breather devices in engines, which separate oil mist from blow-by gas containing the oil mist and allow the blow-by gas with the oil mist removed therefrom to be circulated into intake systems.
2. Description of the Related Art
Generally, in four-cycle engines, blow-by gas leaking into a crank chamber from a combustion chamber by passing through a gap between a cylinder and a piston ring is circulated into an intake system so that the gas can be re-combusted. However, when the blow-by gas leaks into the crank chamber, the gas will contain a mist of lubricating oil in the crank chamber, namely, oil mist. The oil mist is unfavorably carried to the intake system together with the blow-by gas, resulting in increased consumption of lubricating oil as well as having an adverse effect on the engine performance.
In order to solve these problems, there have been proposed various types of breather devices which separate oil mist from the blow-by gas containing the oil mist in the crank chamber so as to supply the blow-by gas having the oil mist removed therefrom to the intake system.
As an example of such a breather device, a breather device disclosed in Japanese Examined Patent Application Publication No. 63-15450 will be described below with reference to a cross-sectional view in FIG. 13.
Specifically, a cylinder head 1101 of an engine includes a head cover 1102 and a side cover 1103. The cylinder head 1101 has a timing-gear chamber 1104 therein, which communicates with a crank chamber (not shown). The timing-gear chamber 1104 communicates with an air cleaner, serving as an intake system, through a breather pipe 1105 provided in the side cover 1103. The cylinder head 1101 rotatably supports a camshaft 1106 therein, whose one end projects into the timing-gear chamber 1104. This projecting end of the camshaft 1106 has a sprocket 1107 attached thereto. The camshaft 1106 is rotated by a crankshaft (not shown) by means of a cam chain 1108 wound between the sprocket 1107 and a sprocket provided on the crankshaft.
On the other hand, a breather device 1110 includes a large-diameter rotating disk 1111 attached to the one end of the camshaft 1106 and a discharge-port member 1112 attached to an inner surface of the side cover 1103. The rotating disk 1111 is positioned closer to the side cover 1103 than the sprocket 1107 is to the side cover 1103. The discharge-port member 1112 disposed on the inner surface of the side cover 1103 includes a shielding plate 1113 functioning as a divider between the side with the timing-gear chamber 1104 and the side with the breather pipe 1105. A central portion of the shielding plate 1113 is provided with a discharge port 1113a through which the timing-gear chamber 1104 and the breather pipe 1105 communicate with each other. The discharge-port member 1112 also includes a cylindrical discharge-port body 1114 that is disposed within the discharge port 1113a and projects towards the rotating disk 1111. The discharge-port body 1114 has a flange portion 1114a at one end thereof, which faces a side surface of the rotating disk 1111.
In the breather device 1110 having the above-described configuration, during an operation of the engine in which the rotating disk 1111 rotates together with the camshaft 1106, blow-by gas is generated in the crank chamber and flows into the breather device 1110. Specifically, the blow-by gas flows through the timing-gear chamber 1104 and passes through a gap 1115 between the rotating disk 1111 and the flange portion 1114a of the discharge-port body 1114. The blow-by gas then travels through the discharge port 1113a so as to be supplied to an air cleaner through the breather pipe 1105. In this case, oil mist contained in the blow-by gas adheres to side surfaces of the rotating disk 1111 and the flange portion 1114a while passing through the gap 1115 due to the viscosity of the oil mist itself, whereby the oil mist is removed from the blow-by gas. The oil mist adhered to the rotating disk 1111 and the flange portion 1114a is scattered due to a centrifugal force generated upon rotation of the rotating disk 1111. The scattered oil mist travels along a wall 1104a of the timing-gear chamber 1104 as droplets so as to return to the crank chamber.
Another example of a breather device disclosed in Japanese Unexamined Patent Application Publication No. 2006-37884 will be described below with reference to FIG. 14.
Specifically, a cylinder head 1120 rotatably supports a camshaft 1125 therein, whose one end is provided with a flange 1126. The flange 1126 has a sprocket 1127 fixed thereto with a mounting bolt 1128. Moreover, the cylinder head 1120 has a breather chamber 1121 located next to a timing-gear chamber 1122. The breather chamber 1121 is formed by a ring-shaped flange 1123 that projects from the cylinder head 1120.
A breather device 1130 is formed by mounting a cylindrical oil separator 1132 onto the sprocket 1127 with a mounting bolt 1133. The oil separator 1132 is formed of a porous plate having a large number of pores 1132a. Subsequently, a breather cap 1135 holding a breather pipe 1129, whose tip end is to be inserted into the oil separator 1132, is mounted onto an outer edge 1123a of the ring-shaped flange 1123 with a mounting bolt (not shown).
In the breather device 1130 having the above-described configuration, during an operation of the engine in which the oil separator 1132 rotates together with the camshaft 1125, blow-by gas generated in the crank chamber flows through the timing-gear chamber 1122 and then passes through the breather chamber 1121 so as to be discharged through the breather pipe 1129. In this case, oil mist contained in the blow-by gas adheres to the oil separator 1132 so as to be removed from the blow-by gas. The oil mist adhered to the oil separator 1132 is scattered due to a centrifugal force generated upon rotation of the oil separator 1132. The scattered oil mist travels along a wall 1122a of the timing-gear chamber 1122 so as to be collected in the crank chamber.
According to Japanese Examined Patent Application Publication No. 63-15450, the blow-by gas generated in the crank chamber flows through the timing-gear chamber 1104 and then passes through the gap 1115 between the rotating disk 1111 and the flange portion 1114a of the discharge-port body 1114 so as to be introduced into an air cleaner through the breather pipe 1105. On the other hand, the oil mist contained in the blow-by gas adheres to the side surfaces of the rotating disk 1111 and the flange portion 1114a having the gap 1115 therebetween, whereby the oil mist is removed from the blow-by gas.
However, because the rotating disk 1111 attached to the camshaft 1106 has a relatively large diameter and the discharge-port member 1112 is large in size, the breather device 1110 occupies a large volume of space. In addition, due to having the shielding plate 1113, the discharge-port member 1112, and the rotating disk 1111, the breather device 1110 has a complex structure and an excessive number of components, which can lead to an increase in cost of manufacture.
On the other hand, in Japanese Unexamined Patent Application Publication No. 2006-37884, the blow-by gas generated in the crank chamber flows through the timing-gear chamber 1122 and then passes through the breather chamber 1121 so as to be discharged through the breather pipe 1129. The oil mist contained in the blow-by gas adheres to the oil separator 1132 so as to be removed from the blow-by gas.
However, because the breather chamber 1121 is formed by the ring-shaped flange 1123 that projects from the cylinder head 1120 having a relatively large size and a complicated shape, the cylinder head 1120 has limited design flexibility. In addition, since the oil separator 1132 is formed into a cylindrical shape using a porous plate, the oil mist adhered to the rotating oil separator 1132 will move along the surface of the rotating oil separator 1132 and will not be able to receive a desired centrifugal force. For this reason, the oil mist may possibly flow into the oil separator 1132 together with the blow-by gas through the pores 1132a. In that case, the oil mist may undesirably be discharged through the breather pipe 1129 together with the blow-by gas. Moreover, the flow rate of the blow-by gas flowing into the oil separator 1132 by passing through the gap between the tip end of the oil separator 1132 and the breather cap 1135 is high. This may be problematic in that a large amount of oil mist may be discharged together with the blow-by gas.